               {:a :_ :b 0 :duration 2} [:js-face :alpha]
               {:a :_ :b 1 :duration 1} [:js-core :alpha]
               {:a :_ :b 2 :duration 2} [:cam :zoom])))
-     (let [t 0.01
-           low 0]
+
+     ;; highlight individual JS versions
+     (let [t 0.01 ;; time between each transition
+           low 0] ;; visited version alpha (faded out)
        [
         #(go
            (<! (animate!

                 {:a :_ :b low :duration t} [:es-captions :es7 :alpha]
                 {:a :_ :b 1 :duration t} [:es-captions :es8 :alpha])))
        ])
     #(go
        (swap! state assoc-in [:transpiler :highlight] true)
        (let [chans [(multi-animate!

(def slide-actions
  "Actions to take for each slide."
  (vec (flatten
    [;; no action for first slide
     nil

     ;; slide in the JS logo
     #(go
        (<! (multi-animate!
              {:a :_ :b 0 :duration 1} [:js-face :x]
              {:a :_ :b 0 :duration 0.4} [:title :alpha])))

     ;; peel back JS logo to see its layers
     #(go
        (<! (multi-animate!
              {:a :_ :b 400 :duration 2} [:cam :x]
